Rust-proofing steel

August 2012 - Rust knows no boundaries, even when it comes to steel. But a team of research chemists at the University at Buffalo, Buffalo, N.Y., have developed a coating to keep corrosion at bay. Using a graphene-based composite solution, scientists found steel plate survived for a month in brine before showing signs of rust.

Graphene is the strongest and thinnest material known, according to University of Manchester professors Andre Grim and Konstantin Novoselov, whose research on graphene earned them the 2010 Nobel Prize in Physics. It’s already been tested for its conductivity and flexibility in electronics and semiconductors. Protection from rust represents a new frontier.

On a molecular level, graphene appears as a two-dimensional mesh latticework of carbon atoms, which, because of the chemical bond’s structure, gives it remarkable strength. Think of it as an extremely resilient honeycomb sheet of carbon atoms.

The researchers pursued graphene as a nontoxic alternative to coatings that contain hexavalent chromium, a suspected carcinogen. “Carbon nanotubes aren’t super environmentally safe, so we’re working with graphene to try and see how it works out,” Banerjee says. “That’s actually been giving us really good performance.”

In the scientists’ first tests, steel samples coated with a hexavalent chromium varnish were immersed continuously in saltwater. The scientists conducted most of the electrochemical testing in about 3.5 percent brine solutions to accelerate corrosion, says Sarbajit Banerjee, Ph.D, assistant professor of chemistry and one of the project’s leading chemists. After a few days, rust began to appear.

After tweaking the concentration and dispersion of graphene in the coating solution, the researchers treated low-alloy steel plate samples. They lasted for nearly a month.

“If you put steel in saltwater and if it’s lasting a long time, that’s a pretty good indication of its ability to protect corrosion,” says Banerjee. The extremely caustic brine environment represents a sped-up variable, so the coated steel’s survival time in real-world use would be much longer.

On a chemical level, the coating works both passively and actively. Passively, it protects the steel’s surface from corroding elements. The active part shuts down some of the electrochemistry that causes rust, Banerjee says.

“Basically, it’s depletion of electrons from the surface so that you don’t have much going on at the steel surface. That’s what our proposed hypothetical mechanism is,” he says.

Coating usesThe coating potentially can be applied in multiple ways. For the experiment, the scientists applied it via wire-bar coating—a method that is fully compatible with an assembly line or coil coating line, Banerjee says. A company could test the coating without investing in capital equipment or new line. The qualities of the solution can be changed so that it could be sprayed on, as well.

“In terms of a commercial coating, we still have a ways to go,” he says.

Tata Steel, Mumbai, sponsored the research and has been helping the scientists test larger sample sizes, according to a university press release. Tata is conducting its own exposure tests on the coating as a part of the research.

Banerjee likens the experiment’s challenges to the Goldilocks effect of dialing in the right chemical composition and ratios of polymer adhesives, which bond the graphene to the steel. “We went in knowing it would be pretty challenging so we’ve been satisfied it’s worked out as well as it has.”

For western New York, a Rust Belt area that’s endured the loss of major steel production during the last several decades, the coating could work with existing operations of local job shops that specialize in chrome electroplating, according to the university. That could help reinvigorate local steel industries around a new and environmentally friendly technology, giving them an edge for a niche application.

“It is more surprising there’s not as much done in the field of corrosion research anymore in the United States,” Banerjee adds. MM